UNITED NATIONS -LRB- CNN -RRB- -- World leaders , many reeling from a year marked by global economic freefall and a growing threat from global warming and nuclear proliferation , exhorted one another Wednesday to work together to meet those challenges .

Libyan leader Moammar Gadhafi addresses the U.N. General Assembly on Wednesday .

In his first remarks to the U.N. General Assembly , President Obama noted that he took office last January `` at a time when many around the world had come to view America with skepticism and distrust . ''

He then sought to distance himself from the policies of his predecessor , noting that he had prohibited the use of torture , ordered the prison at Guantanamo Bay to be closed and has been working to create a framework to combat terrorism `` within the rule of law . ''

Obama called on world leaders to work together to effect the change needed . `` No longer do we have the luxury of indulging our differences to the exclusion of the work that we must do together , '' he said .

He vowed to pursue an agreement with Russia to reduce the number of nuclear weapons , to combat nuclear smuggling and theft and to support the non-proliferation treaty . Watch President Obama speak to the United Nations ''

He identified North Korea and Iran as countries whose governments `` threaten to take us down this dangerous slope '' and said he is committed to diplomacy in persuading them to live up to their obligations .

Obama called for `` more progress '' in the Middle East . `` We continue to call on Palestinians to end incitement against Israel and we continue to emphasize that America does not accept the legitimacy of continued Israeli settlements , '' he said to applause .

Obama left no doubt that he believes the danger posed by global warming is a real one . `` Our responsibility to meet it must not be deferred . If we continue down our current course , every member of this assembly will see irreversible changes within their borders , '' he said .

Libyan leader Moammar Gadhafi also called for world unity in confronting crises -- such as climate change and food shortages -- but he expressed ire at the world body and the United States . Watch Gadhafi 's rant at the U.N. ''

In a 96-minute , rambling address in his first appearance before the United Nations , Gadhafi broached conspiracy theories , urged probes into U.S. military activities and took aim at the structure and the actions of the Security Council itself .

Dressed in a traditional Libyan cap and robe , he elaborated on what he said is the unfairness of the structure of the U.N. Security Council , which has five permanent members -- the United States , Russia , China , France and Britain , each with veto power .

`` Are we equal in permanent seats ? '' Gadhafi asked . `` No , we 're not equals . ''

He said the Security Council has provided not security , but `` terror and sanctions . '' No one should accept the resolutions of the Security Council , he said , adding that the body should be called the `` terror council . '' Watch Gadhafi demand equality ''

He also slammed U.S. military actions in places such as Panama , Vietnam and Grenada and called the invasion of Iraq `` the mother of all evils . ''

On the Middle East , he said the solution for Israelis and Palestinians `` is a democratic state without religious fanaticism '' and said people on both sides want to live in one state .

Still , Gadhafi referred to Obama as `` my son , '' and congratulated him on his first U.N. General Assembly speech . Watch demonstrators for and against Gadhafi ''

Iranian President Mahmoud Ahmadinejad announced he is ready to work with other nations .

`` Our nation is prepared to warmly shake all those hands that are honestly extended to us , '' he told the assembly . `` We welcome real and human exchanges and stand ready to actively engage in fundamental global reforms . ''

He called for a `` return to monotheism and justice , '' calling it `` the greatest hope and opportunity in all ages and generations . ''

Ahmadinejad blamed the world economic crisis on capitalism , saying , `` It is no longer possible to inject thousands of billions of dollars of unreal wealth into the world economy simply by printing worthless paper . ''

He added , `` The engine of unbridled capitalism , with its unfair system of thought , has reached the end of the road and is unable to move . ''

He added that the time has passed for those people who outwardly espouse democracy and freedom yet who are simultaneously `` violating the very principles to which they aspire . ''

Ahmadinejad then cited the United States , one of several countries critical of his country 's nuclear ambitions , despite Iran 's insistence that its program is intended solely for peaceful purposes .

He was critical of the situations in Gaza as well as in Iraq and Afghanistan , where `` thousands of innocent people have been killed , injured or displaced , infrastructures have been destroyed and regional security has been seriously jeopardized . ''

By this time , the U.S. and Israeli representatives had left their seats . Watch representatives leave their seats ''

Before his talk , and blocks away from the United Nations , more than 400 protesters toted anti-Ahmadinejad banners and demonstrated in front of the Iranian U.N. Mission .

`` I am very angry , '' said Anna Amiri , an Iranian emigre who traveled from Dallas , Texas , to attend the rally . `` We voted for Moussavi to have a change , '' she said , referring to Mir Hossein Moussavi , Ahmadinejad 's main opponent in the election .

The results released by Iran said Ahmadinejad won by a wide margin , a conclusion that sparked street protests and violence . Watch Iranian student tell Ahmadinejad `` Be afraid '' ''

At the U.N. , French President Nicolas Sarkozy referred to Iran 's leaders in his address , saying , `` If they rely on a passive response from the international community in order to pursue their military nuclear program , they will be making a tragic mistake . ''

Addressing global warming and the economic crisis , Sarkozy said the world is on the threshold of an ecological disaster and called on its leaders to `` invent a new world where the follies of yesterday '' can not be repeated .

Sarkozy said the world has already waited too long for globalization to be regulated , global warming to be fought and nuclear proliferation to be curbed .

He called for the Security Council to be expanded to include an African nation , a South American nation , India , Japan and Germany as permanent members .

`` The legitimacy of the United Nations depends on this reform , '' he said .

He further called for reform of the International Monetary Fund and the World Bank and urged that their mission be redefined in the wake of the world economic crisis .

In his address , British Prime Minister Gordon Brown listed climate change , terrorism , nuclear proliferation , shared prosperity and the need to eradicate poverty as key issues that must be addressed .

`` We must grasp this next set of challenges immediately , '' he said .

Russian President Dmitry Medvedev , noting that 2010 marks the 65th anniversary of the end of World War II , took aim at those who deny the Holocaust happened and called for `` firm and joint resistance to manifestations of neofascism . ''

He described Russia as prepared to `` follow the path of reductions of nuclear weapons . ''

In the annual session 's opening address , U.N. Secretary-General Ban Ki-moon urged global leaders to work together to face many of the world 's challenges : `` Now is our time . A time to put the ` united ' back into the United Nations . United in purpose . United in action . ''

He called for tackling `` the threat of catastrophic climate change '' and expressed hope that nations will succeed in dealing with the problem if they work together .

He touched on nuclear disarmament , too , saying , `` Let us make this the year we agreed to banish the bomb . ''

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NEW : Leaders from Obama to Gadhafi discuss climate change , disarmament

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U.S. , Israeli representatives leave seats during Iranian president 's address

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Libyan leader Moammar Gadhafi says U.N. Security Council brings terror , not security

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Global challenges require unified action , U.N. secretary-general says